Paper board crease force measuring device

ABSTRACT

An apparatus and method for determining the crease characteristics of a corrugated paper board sample including a sample location area, a load cell located such that a portion of the surface of the sample overlies the load cell, and a creasing edge which abuts a portion of the sample on the surface opposite the surface which overlies the load cell. Thus the portion of the sample opposite the load cell can be manually lifted to crease the product about the creasing edge, causing the portion of the sample which overlies the load cell to bear against the load cell, and with the force being measured by the load cell.

This invention relates to an apparatus and method for measuring thecreasing characteristics of paper board.

In high speed box making machines and automated packing lines it isimportant that the consistency and quality of creases is closelycontrolled and maintained. If this is not done successfully thepotential to form false creases in paper board which can cause thejamming of machines or the production of malformed boxes is increased.

Thus it is important to be able to assess the variation in creasingcharacteristics in different types of paper board. The characteristicsof interest include the peak force required to fold the board, the ratioof forces required to fold creased and uncreased board and the forcerequired to fold the board at a predetermined angle.

The measurement of the peak force required to fold the paper board isuseful in assisting the box maker to assess the quality of the board andtherefore the parameters under which box production can occur withminimal jamming and production of malformed boxes.

The determination of the peak force generated at a specified angleduring the folding of paper board can also be useful to know forspecific operations. Some packing machines only fold the crease througha small angle --less than the angle at which the maximum force willoccur. If this smaller force proves to be a significant fraction of theforce required for uncreased board there is the possibility that anuncreased part of the board will fold rather than the crease itself,leading to deformation of the box and runnability problems.Alternatively, if the force at the required angle is much less than theuncreased paper board creasing force then there will be noproblem--independent of whether the peak force is close to the uncreasedboard creasing force or not.

The ratio of forces required to fold creased and uncreased boardprovides a useful assessment of the potential to form false creases. Inorder to determine the quality of creases in a board sample, a ScoreBend Test has been used for quantifying "crease quality". It involvesthe measurement of the force required to fold a creased line and themeasurement of the force required to fold an uncreased line parallel tothe crease. Usually, the crease quality is expressed as a % Score Ratioor a foldability coefficient which is calculated as the ratio of thepeak folding force of the creased board to the peak folding force of theuncreased board.

As the measurement of peak folding force, peak force at an angle and thecalculation of the % Score Ratio to determine the crease quality ofboard is important in the manufacture of boxes and board products therehave been numerous attempts to develop a machine which measures creasequality and other characteristics of both corrugated boards and cartonboards quickly and easily.

In one conventional instrument for measuring these forces, the specimenis placed across the top of a "Y-shaped" support and a pressure bar issituated above the support. The Y-shaped support moves upwardscontrolled by a motor such that the test specimen is forced against thepressure bar which is connected to a mechanical force gauge. Thepressure bar must be positioned either over the score line of a creasedsample or over the flute tip of the corrugations of an uncreased sample.Such machines are cumbersome and time consuming to use because thesample must be positioned on the support and aligned very carefully.Misalignment of the sample will lead to an inaccurate result. Thesemachines are also fairly complicated because they require a motor tomove the Y-shaped support. They are also bulky which is not desirable inmanufacturing plants, due to the requirement that the apparatus becombined with a motor.

Additionally there have been other types of apparatus proposed whichmeasure the flexural resistance of board products. The flexuralresistance measurements provide an indication of the boards tendency tobuckle under load which is an important characteristic to consider whenthe board is to be used in industrial packaging operations. U.S. Pat.No. 5,106,477 describes an apparatus for measuring the flexuralresistance of ribbed cardboard, for example, corrugated board. Thepatent discloses an apparatus wherein an uncreased corrugated boardsample is clamped between two supports, the two supports and theuncreased sample are then moved by a motor upwards such that theuncreased sample comes into contact with a roller connected to a loadcell. As the uncreased sample connects with the roller, it is bent andthe force required to bend the uncreased sample is recorded by the loadcell. The apparatus disclosed in the U.S. patent is only designed tomeasure the flexural resistance of an uncreased sample. This machinehowever, is also complicated and time consuming to use. It too requirescareful placement of the sample between two clamps which must then besuitably tightened. The machine requires a motor to move the sample intocontact with the roller which is bulky and increases the likelihood ofproblems with operation of the machine.

Because of these difficulties the proposed apparatus have not beenwidely used for measuring crease quality and other characteristics ofboard products. The most commonly used measure of crease quality is foran experienced box-maker to wave a sample in his hand and observe theease of forming a fold line.

It is an object of this invention to overcome at least some of thesedisadvantages of the prior art by providing a simple apparatus formeasuring the crease quality and other characteristics of paper boardwhich is quick and easy to use.

The invention therefore provides an apparatus for determining the creasecharacteristics of a corrugated paper board sample including

a sample location area;

a load cell located such that a portion of the surface of the sampleabuts the load cell; and

a creasing edge which abuts a portion of the sample on a surfaceopposite to the surface which abuts the load cell.

In general, it is preferred that the portion of the sample on the sideof the creasing edge remote from the load cell is adapted for rotationtoward the load cell and it is also preferred that the creasing edgeabout which the sample is bent remains stationary with respect to theload cell during measurement. Thus, it is particularly preferred thatthe force measured by the load cell is exerted on the load cell in thesame rotational direction as the force exerted on the sample.

It is also preferred that the sample is bent about the creasing edgemanually and is therefore not mechanically or electrically driven.

Furthermore, the invention also provides a method for determining thecrease characteristics of a corrugated paper board sample including

loading the sample in a sample location area;

bending the sample about a creasing edge such that the portion of thesample on the side of the creasing edge remote from the load cell isrotated towards the load cell; and

measuring the force required to bend the sample with the load cell.

It is preferred that during the determination of the force required tobend the sample around the creasing edge, the creasing edge remainsstationary with respect to the load cell. It is also preferred that thesample is folded about the creasing edge manually.

The load cell is any device capable of measuring an applied force withina suitable range i.e. from 0 to 50 newton. The load cell may be locatedabove, below or to the side of the portion of the board sample abuttingit.

The creasing edge may take the form of a bar or a wedge, however, asthose skilled in the art would aware it can also take the form ofequivalents such as a piece of wire or lugs located at either edge of asample to commence the crease. Depending on the location of the loadcell relative to the sample, the creasing edge may form part of thesample location area.

Thus the invention advantageously provides an apparatus and a method forthe determination of crease characteristics of a sample of paper boardquickly and easily. The apparatus is easy to operate allowing for therapid repetition of tests. When manually operated, the apparatus iscompact, portable and has minimal power requirements.

The invention is, in part, predicated on the discovery that the maximumforce required to fold a crease is independent of the rate at which thecrease is folded. It is therefore preferable that there be no form ofcontrol over the rate at which the board is bent. It is not necessary touse a motor to provide a constant and consistent rate for the folding ofa sample, thus resulting in lower running costs and a more compactdesign. In contrast to all prior art instruments for measuring creaserelated properties the sample is bent over the crease edge in the samedirection as the force measured by the load cell.

A preferred embodiment of this invention will now be described withreference to the following figures:

FIG. 1 shows a schematic view of the apparatus according to theinvention;

FIG. 2 shows a diagram of the apparatus according to the invention;

FIG. 3 shows a functional flow chart for the apparatus according to theinvention; and

FIG. 4 shows a test function flow chart for the apparatus according tothe invention.

The apparatus comprises a paper board sample location area (1) whichconsists of an arm (5) and a load cell table (2). The load cell (3) islocated under the load cell table (2) so that the force exerted by thepaper board sample (4) (shown in FIG. 1 only) on the load cell table (2)can be measured by the load cell (3). The apparatus also comprises acreasing edge (6) about which the sample is folded during testing. Theload cell is connected to a computer or microprocessor which is capableof taking numerous measurements, recording, storing and analysing theresults. The apparatus may be connected to a printer to enable theinformation obtained to be printed. FIG. 3 shows the force foldingtester functional flow chart--(PSU refers to power supply unit). Theoperation of the tester may be divided into four sections: sampleidentification, serial output, option menu and calibration.

The apparatus can be used to perform the following tests:

PEAK FORCE TEST

To maintain maximum efficiency on high speed box making machines andautomated packing lines, the quality of creases must be controlled. Theapparatus subject of this invention provides a quick, easy andrepeatable assessment of crease quality.

The folding force tester shown in FIG. 2 allows for the manual foldingof both creased and uncreased corrugated paper board. The fold may bemade in both the cross direction ie., parallel to the flutes or in themachine direction ie., at right angles to the flutes. The test folds theboard about 90° from the planar position. The peak force generated bythe test sample (not shown) during the folding action is measured by theload cell (3) and is displayed on the display of the tester (7). Thepreferred load cell is an XTRAN 100N load cell which is obtained fromApplied Measurement.

To carry out the test a template is required for cutting 100 mm widestrips of paper board. The sample should be at least 100 mm wide so thatthe crease position (either previously creased or not) lies squarelyacross the 100 mm width. The sample should be at least 150mm long, andpreferably 200 mm long, cut so as to provide a distance between one endof the sample and the crease position of 120 mm.

It is important to avoid unnecessary stressing of the crease positionbefore testing. Designate and record the position of the crease positionin the box blank or sheet on the sample with a felt tip pen to avoiddamaging it. It is possible that creases in various positions on a boxblank may be designed purposely to give different folding force results.The level of folding force results will also depend upon the paper boardgrade being tested.

Prepare at least four equivalent test pieces for the nominated creaseposition. These should be taken from identical box blanks at the sameposition in the blank. Then calibrate the folding force tester ifnecessary.

Place the 120 mm length of the sample on the sample location area (1)such that the crease position is located directly below the creasingedge (6). Generally, the sample should be placed so that the insideliner of the box is facing upwards during testing. However, for somepackaging machine operations it may be necessary to test with the insideliner facing down.

Place a hand under the lip of the arm (5) and smoothly lift the armthrough an arc until the movement is arrested by a hinge stop (notshown). Immediately return the arm to the horizontal position. As thearm is returned to the horizontal position the peak folding force willbe displayed on the display (7) and will continue to be displayed untilthe next sample is tested. The angle at which the peak force occurs isalso displayed.

Repeat this test for all samples. As the series of tests progresses, thelast test value, the mean value and the standard deviation of the testseries and N, the number of tests are shown on the tester display (7).The peak force is measured in newtons and the apparatus in general canmeasure between 0 and 30 newtons. The resolution of the measurements isin the order of 0.01 newton.

THE SCORE TEST RATIO

The score test ratio reports the ratio of the maximum force generated bythe folding of creased board to that when folding uncreased board. Thisis used to allow box makers to take into account the variation betweendifferent types of boards when measuring crease resistance to folding.This test provides for the quantifying of the degree of creasing or thedamage incurred by the board during the creasing process.

The score test ratio is defined as follows: ##EQU1##

Prepare the samples as described above (Peak Force Test) but preparingat least four equivalent pairs (creased/uncreased) of samples for thenominated crease position. These should be taken from identical boxblanks as close as possible to the same position in the blank. It isimportant to avoid unnecessary stressing of the crease before testing.Calibrate the apparatus if necessary.

In response to the display (7) flashing TEST THE CREASED BOARD, placethe 120 mm length of the creased sample on the sample location area (1)such that the crease is positioned directly below the creasing edge (6).Generally, the sample should be placed so that the inside liner of thebox is facing upwards during testing. However, for some packagingmachine operations it may be necessary to test with the inside linerfacing down.

Place a hand under the lip of the arm (5) and smoothly lift the armthrough an arc until the movement is arrested by a hinge stop (notshown). Immediately return the arm to the horizontal position. As thearm is returned to the horizontal position the display will ask for theuncreased board sample for testing.

Insert the uncreased board sample, ensuring that the orientation of theuncreased sample is identical to the corresponding creased sample.Repeat the procedure for all the creased and uncreased sample pairs. Asthe series of tests progresses, the last test ratio, the mean value andstandard deviation of the test series and N, the number of tests areshown on the tester display.

FIG. 4 shows the test function flowchart for determining the peak forceor the score ratio.

PEAK FORCE AT ANGLE

The determination of the peak force at a specified angle can be done byselecting the "at angle" test. This can be useful if a particular angleis meaningful in a specific operation. When selecting this test, theoperator is prompted to enter the angle at which the force is to bemeasured. The apparatus has a sensor located at the point of rotation ofthe sample which records the angle and correlates this to the forcerecorded by the load cell.

Prepare the samples as described above (Peak Force Test). These shouldbe taken from identical box blanks as close as possible to the sameposition in the blank. It is important to avoid unnecessary stressing ofthe crease before testing. Calibrate the apparatus if necessary.

Place the 120 mm length of the sample on the sample location area (1)such that the crease is positioned directly below the creasing edge (6).Generally, the sample should be placed so that the inside liner of thebox is facing upwards during testing. However, for some packagingmachine operations it may be necessary to test with the inside linerfacing down.

Place a hand under the lip of the arm (5) and smoothly lift the armthrough an arc until the movement is arrested by a hinge stop (notshown). Immediately return the arm to the horizontal position. Theresult is reported on the display, indicating the force at a particularangle as well as the mean and standard deviation for the series oftests. If desired, the output can be graphed on a FORCE vs ANGLE plotwhich may be useful when the shape of the force plot is required foranalysis.

The claims defining the invention are as follows:
 1. An apparatus fordetermining the crease characteristics of a corrugated paper boardsample, said apparatus comprising:a sample location area; a load cellfor measuring an applied force, said load cell being located within saidsample location area such that one surface of a sample positioned on thesample location area overlies the load cell; and a creasing edgepositioned to transversely overlie the sample location area at alocation laterally spaced from the load cell, wherein the creasing edgeis adapted to transversely overlie the opposite surface of a samplepositioned on the sample location area, and wherein a portion of thesample on the side of the creasing edge remote from the load cell can berotated about the creasing edge towards the load cell, such that theforce exerted on the load cell is in the same rotational direction asthe force exerted on the sample.
 2. An apparatus as claimed in claim 1wherein the creasing edge about which the sample is bent remainsstationary with respect to the load cell during measurement.
 3. A methodfor determining the crease characteristics of a corrugated paper boardsample, said method comprising the steps of:loading the sample in asample location area such that a surface of the sample overlies a loadcell, and such that a surface opposite the surface which overlies theload cell is adjacent a creasing edge which is laterally spaced from theload cell; bending the sample about the creasing edge such that theportion of the sample on the side of the creasing edge remote from theload cell is rotated towards the load cell and the force exerted on theload cell is in the same rotational direction as the force exerted onthe sample; and measuring the force required to bend the sample with theload cell.
 4. A method according to claim 3 further comprisingmaintaining the creasing edge stationary with respect to the load cellduring said measuring step.
 5. A method according to claim 3 wherein thestep of bending the sample comprises bending the sample manually.
 6. Amethod according to claim 3 comprising the further step of calculating ascore test ratio by determining the ratio of the peak folding force of acreased sample to the peak folding force of an uncreased sample.